Electrical safety monitoring system utilizing a heartbeat signal indicative of voltage present on line inputs

ABSTRACT

An electrical safety monitoring system is provided. The system includes an analog circuit having line inputs for hardwiring an L1, an L2, an L3, and a GND three-phase connections, the analog circuit configured to monitor if voltage exists between any two of the line inputs, a heartbeat circuit electrically connected to the analog circuit to provide a heartbeat signal indicative of voltage present on any of the line inputs, an isolated voltage source electrically connected to the heartbeat circuit to power the heartbeat circuit with a VDC+ and a VDC−, and a logic circuit in operative communication with the heartbeat circuit for monitoring input from the heartbeat circuit and decoding the input from the heart beat circuit. The isolated voltage source may be supplied by a programmable logic controller (PLC) and the logic circuit may be implemented within the same PLC as a function block.

PRIORITY STATEMENT

This application claims priority to U.S. Provisional Patent ApplicationNo. 62/585,891 filed on Nov. 14, 2017 which is hereby incorporated byreference in its entirety.

FIELD OF THE INVENTION

The present invention relates to electrical safety devices. Moreparticularly, but not exclusively, the present invention relates tointerfacing with an analog circuit for voltage monitoring and conveyingstate information in a safe and effective manner.

BACKGROUND

The present invention relates to electrical safety, and moreparticularly to monitoring of AC voltages using voltage indicators. Avoltage indicator is generally a low cost device that pre-verifieselectrical isolation before maintenance personnel open a control paneland risk exposure to hazardous voltages. Typically mounted to the panelexterior and hardwired into the load side of the main disconnect, thisdevice provides electrical maintenance with an additional safety valve.Easy to apply, low cost, quick installation, and inherent reliabilitymakes a voltage indicator a very effective electrical safety device.

Creating and insuring an electrically safe work condition is criticalfor electricians performing maintenance on de-energized systems. Thepresence of voltage is the only determining factor if an electricalaccident or an arc flash can possibly occur—No voltage, No accident, Noarc flash. “Voltage or no voltage” is also the basis of the NFPA 70E's(National Fire Protection Association Standard's for Electrical SafetyRequirements for Employee Workplaces) two primary themes: a)establishing an electrically safe work condition, and b) achievingsafety while working on energized systems. A voltage warning indicatoris like a ‘hard wired voltmeter’ with the advantage that it needs nopower supply or batteries because it is powered from the same ‘voltage’that it indicates. A voltage indicator is an additional safety measurebetween maintenance personnel and hazardous voltage.

One example of an electrical safety device is a thru-door voltageindicator such as the R-3 W thru-door voltage indicate from GraceEngineered Products, Inc. of Davenport, Iowa. Such a device provideselectrical safety information while the panel doors are safely closed.In particular, an individual can view the voltage indicator from outsidethe enclosure and while the panel door is closed. Such a device maydetect 3-phase AC or DC voltage such as from 40-750 VAC and 30-1000 VDC.This is a significant range. Such a device is an analog circuit. Theanalog circuit being used may be of the type disclosed in U.S. Pat. No.6,703,938 to Clarke, hereby incorporated by reference in its entirety.

Despite the advantages of such a device, problems remain. In particular,it would be advantageous if such an analog based design could beinterfaced in a safe and effective manner with other circuitry, thenstate information could be used in additional lock-out tag-outprocedures, could be remotely monitored, or other benefits could beobtained. However, there are issues with interfacing such a circuit withother devices. In particular, the interface should not have any adverseeffect on the operation of the monitoring circuit. In addition, such ananalog circuit has high impedance and a limited ability to create usefulenergy. Moreover, the interfacing circuit needs to result in accurateconveyance of the presence or absence of voltage and its presenceintroduces another failure point and so provision must be made forsituations where the interfacing circuit itself fails.

SUMMARY

Therefore, it is a primary object, feature, or advantage of the presentinvention to improve over the state of the art.

It is a further object, feature, or advantage of the present inventionto interface with an analog circuit of an electrical safety device.

It is a still further object, feature, or advantage of the presentinvention to communicate state of line inputs from an electrical safetydevice.

One or more of these and/or other objects, features, or advantages ofthe present invention will become apparent from the specification andclaims that follow. No single embodiment need provide each and everyobject, feature, or advantage. Different embodiments may have differentobjects, features, or advantages. Therefore, the present invention isnot to be limited to or by an objects, features, or advantages statedherein.

According to one aspect, an electrical safety monitoring system isprovided. The system includes an analog circuit having line inputs forhardwiring an L1, an L2, an L3, and a GND three-phase connections, theanalog circuit configured to monitor if voltage exists between any twoof the line inputs, a heartbeat circuit electrically connected to theanalog circuit to provide a heartbeat signal indicative of voltagepresent on any of the line inputs, an isolated voltage sourceelectrically connected to the heartbeat circuit to power the heartbeatcircuit with a VDC+ and a VDC−, and a logic circuit in operativecommunication with the heartbeat circuit for monitoring input from theheartbeat circuit and decoding the input from the heart beat circuit.The isolated voltage source may be supplied by a programmable logiccontroller (PLC) and the logic circuit may be implemented within thesame PLC as a function block. The heartbeat signal may take on anynumber of forms such as where information for the line inputs isrepresented through duty cycle.

According to another aspect, a method of electrical safety monitoring isprovided. The method includes monitoring an L1, an L2, an L3, and a GNDthree-phase connections with an analog circuit, the analog circuitconfigured to monitor if voltage exists between any two of the lineinputs, generating at heartbeat signal indicative of voltage present onany of the line inputs, and monitoring the heartbeat signal and decodingthe heartbeat signal to provide status of the three-phase connections.

According to another aspect, a method of electrical safety monitoringincludes monitoring line inputs consisting of an L1, an L2, an L3, and aGND three-phase connections with an analog circuit, the analog circuitconfigured to monitor if voltage exists between any two of the lineinputs. The method further includes generating at heartbeat signalindicative of voltage present on any of the line inputs using aheartbeat circuit, wherein the heartbeat circuit is electricallyconnected to an isolated voltage source to power the heartbeat circuitwith a VDC+ and a VDC−. The method further includes monitoring theheartbeat signal and decoding the heartbeat signal to provide status ofthe three-phase connections and detect interruptions between theisolated voltage source and the heartbeat circuit. The heartbeat circuitmay be electrically connected to an isolated voltage source to power theheartbeat circuit with a VDC+ and a VDC−. The heartbeat signal varies induty cycle based on whether or not voltage is detected at any of theline inputs. The heartbeat signal may vary in amplitude based onamplitude of voltage detected at any of the line inputs and varies induty cycle based on whether or not voltage is detected at any of theline inputs.

BRIEF DESCRIPTION OF THE DRAWINGS

Illustrated embodiments of the disclosure are described in detail belowwith reference to the attached drawing figures, which are incorporatedby reference herein.

FIG. 1 illustrates one example of an electrical safety monitoringsystem.

FIG. 2 illustrates another example of an electrical safety monitoringsystem where a wireless transceiver is used.

FIG. 3 illustrates another example of an electrical safety monitoringsystem where a switch is used.

FIG. 4 illustrates one example of an analog circuit.

DETAILED DESCRIPTION

One example of an electrical safety device is a thru-door voltageindicator such as the R-3 W thru-door voltage indicate from GraceEngineered Products, Inc. of Davenport, Iowa. Such a device provideselectrical safety information while the panel doors are safely closed.In particular, an individual can view the voltage indicator from outsidethe enclosure and while the panel door is closed. Such a device maydetect 3-phase alternating current (AC) or direct current (DC) voltagesuch as from 40-750 VAC and 30-1000 VDC. This is a significant range.Such a device is an analog circuit, but there is a need to interfacesuch a circuit to other devices. The analog circuit being used may be ofthe type disclosed in U.S. Pat. No. 6,703,938 to Clarke, herebyincorporated by reference in its entirety. Such an analog circuit may ofthe type shown in FIG. 4. The present invention provides interfacingsuch an analog-based design in a safe and effective manner, so as togenerate state information which may be used in additional lock-outtag-out procedures, may be remotely monitored, or other createsbenefits. It should be appreciated that any benefits provided by thefeatures of the invention described herein may be significant andsubstantial in improving electrical safety and thus highly desirable.

FIG. 1 illustrates one example of an electrical safety monitoring system10 with a housing 11. The system 10 includes an analog circuit 12 havingline inputs for hardwiring an L1, L2, L3, and a GND three-phaseconnection. The analog circuit is configured to monitor if voltage exitsbetween any two of the line inputs. A heartbeat circuit 16 iselectrically connected to the analog circuit to provide a heartbeatsignal 17 indicative of voltage present on any of the line inputs. Anisolated voltage source 18 is electrically connected to the heartbeatcircuit 16 to power the heartbeat circuit 16. A logic circuit 14 such asmay be associated with a control system is operatively connected to theheartbeat circuit 16 for monitoring input from the heartbeat circuit 16and decoding the input from the heartbeat circuit.

The heartbeat signal may be of any number of different types of signal.For example, if there is voltage detected the signal may be set to VDC+for half of a cycle and to VDC− for half of a cycle. Thus, where x isthe total cycle time of the heartbeat signal, the signal is set to VDC+for x/2 time and set to VDC− for x/2 time. If there is an absence ofvoltage then the signal may be set to a different value. For example, ifthere is absence of voltage then the signal may be set to VDC+ for aquarter of a cycle and VDC− for a quarter of a cycle. Thus, where x isthe total cycle time of the heartbeat signal, then signal may be set toVDC+ for x/4 and set to VDC− for (3*x)/4. Thus, the duty cycle of theheartbeat signal may be used to encode state information for the lineinputs being monitored.

The heartbeat signal may also vary by voltage. For example, theheartbeat signal may be set to VDC+ for x/(y*2) time and set to VDC− forx/(y*2). Here, x would be the total cycle time of the heartbeat signalwhereas y would vary based on the voltage level that the analog circuitdetects. The higher the voltage the larger y would be. For example, ycould vary between 1 and 100. This would allow a range that thereceiving device would be able to detect if the voltage is towards thelower range, the middle range, or the upper range. The lower the voltagethe lower y would be. If there is an absence of voltage then the signalmay be set to VDC+ for x/4 and set to VDC− for (3*x)/4. Thus, varyingthe voltage or amplitude may be performed in order to encode informationabout the line inputs. Of course, it is to be understood that any numberof other schemes may be used in order to convey the presence of voltage,the absence of voltage, and/or the magnitude of voltage detected.

The heartbeat circuit 16 used is based upon the manner desired forrepresenting the presence or absence of voltage and/or the magnitude ofvoltage. The heartbeat circuit may include a timer circuit, anoscillator circuit, or other types of circuits to vary cycling and/oramplitude.

If the VDC voltage from the voltage source 18 was interrupted to theanalog heartbeat circuit 16 such as due to a broken wire or connection,this would be detected because the heartbeat signal would not go high(to VDC+). Similarly, if the VDC-wire or connection was broken, theheartbeat signal would not go low (to VDC−). Thus, if there is a brokenwire or connection, this may be determined from the heartbeat signal.

FIG. 2 illustrates an alternative embodiment. In FIG. 2 the heartbeatsignal may be communicated to a wireless transceiver 20. The wirelesstransceiver 20 may then generate a wireless signal to communicate theheartbeat signal indicative of the status of voltage. The wirelesstransceiver 20 may be a wireless radio transceiver of any of a number ofdifferent types of wireless radio transceivers. This may include Wi-Fi,Zigbee, Bluetooth, Bluetooth Low Energy (BLE), Z-Wave, or other type ofwireless connection. Another receiver or transceiver 20 may be used toreceive the heartbeat signal. Instead of having the heartbeat signaldecoded at the transceiver 20, the heartbeat signal may be decoded atthe receiver or transceiver 22.

Note that in FIG. 2, the VDC+ and VDC− connections to a voltage sourcesuch as a PLC are still present. These connections may be used todetermine that the voltage source or PLC is still connected to theanalog circuit 12 and if the voltage source or PLC is not connected tothe analog circuit 12 of the voltage indicator, the analog circuit maysignal that it lost the voltage connections through the wirelessconnection. The analog circuit may monitor the voltage in the mannerpreviously described, however, instead of sending the status over wiresback to a PLC, it may send the heartbeat signal over the wirelessconnection. The heartbeat signal may go back to the device that isreceiving the wireless connection. The device may be a smartphone,tablet, computer, or other type of computing device. Software operatingon the device may receive the heartbeat signal and determine the stateof the voltage indicator from the signal. These states may includevoltage unsafe, absence of voltage, loss of power from the PLC, andother states. If a switch is present as will be discussed, the state ofthe switch as being open or closed may also be included. In addition,transitions associated with the switch may be communicated. For example,if the switch just opened the device could determine that there shouldbe an absence of voltage and indicate whether or not that conditionoccurred as expected. If not, it could indicate an error state. Thedevice may also indicate a safe state if the switch opened and there isan absence of voltage. The wireless communication protocol may bedefined to send redundant communication messages for each criticalsignal. The redundant messages may be checked and if found to be valid,then an interpretation of the signal may be displayed on the device. Ifthe redundant messages are found to be invalid, then the device may showan error or else ignore the message. It should be understood that theinterpretation of the signal performed by the device may be performedusing software and may be configured differently for differentapplications.

FIG. 3 illustrates another implementation where a separate voltage 18from a PLC or otherwise may pass through auxiliary contacts 26, 28 of adisconnect switch 32 and/or circuit breaker 30 (hereinafter “switch”).This allows for an indication to the analog circuit 12 that the switchhas opened. There may be two auxiliary contacts for redundancy. Eachcontact may go to a separate input on the analog circuit 14 for thevoltage indicator. One contact may be normally open and the othercontact may be normally closed. This allows the analog circuitry 12 ofthe voltage indicator to determine if the switch just opened or justclosed. This also allows the voltage indicator to detect if there was afailure in one of the contacts as both contacts cannot be in the samestate. This failure may be further reflected by the heartbeat signal 17being sent. The voltage indicator may then create the signal in themanner previously described.

The invention is not to be limited to the particular embodimentsdescribed herein. In particular, the invention contemplates numerousvariations in the analog circuit, the heartbeat circuit, the logiccircuit, the manner in which the state of the line inputs is conveyed,and numerous other variations. The foregoing description has beenpresented for purposes of illustration and description. It is notintended to be an exhaustive list or limit any of the invention to theprecise forms disclosed. It is contemplated that other alternatives orexemplary aspects are considered included in the invention. Thedescription is merely examples of embodiments, processes or methods ofthe invention. It is understood that any other modifications,substitutions, and/or additions can be made, which are within theintended spirit and scope of the invention.

What is claimed is:
 1. An electrical safety monitoring systemcomprising: a housing; an analog circuit disposed within the housing andhaving line inputs for hardwiring a first line (L1), a second line (L2),a third line (L3), and a ground (GND), wherein each of the line inputsis a three-phase connection, wherein the analog circuit is configured tomonitor if voltage exists between any two of the line inputs and furtherconfigured to visually indicate presence or absence of voltage on eachof the line inputs; a heartbeat circuit electrically connected to theanalog circuit to provide a heartbeat signal indicative of voltagepresent on any of the line inputs, the heartbeat signal encoding stateinformation for the line inputs; an isolated voltage source electricallyconnected to the heartbeat circuit to power the heartbeat circuit with aVDC+ and a VDC−; a logic circuit in operative communication with theheartbeat circuit for monitoring input from the heartbeat circuit anddecoding the input from the heartbeat circuit to determine stateinformation for the line inputs; wherein the heartbeat signal is set tothe VDC+ for a first portion of a cycle and to the VDC− for a secondportion of the cycle if there is voltage detected at any of the lineinputs according to a first ratio which represents a ratio of the firstportion to the second portion; wherein the heartbeat signal is set tothe VDC+ for the first portion of the cycle and to the VDC− for thesecond portion of the cycle if there is no voltage detected at any ofthe line inputs according to a second ratio which also represents aratio of the first portion to the second portion, the second ratiodifferent from the first ratio.
 2. The system of claim 1 wherein theisolated voltage source is supplied by a programmable logic circuit(PLC).
 3. The system of claim 1 wherein the heartbeat signal varies inamplitude based on amplitude of voltage detected at any of the lineinputs.
 4. The system of claim 1 further comprising a wirelesstransceiver electrically connected to the heartbeat circuit forreceiving the heartbeat signal and wherein the logic circuit is locatedremotely from the heartbeat circuit.
 5. The system of claim 4 whereinthe wireless transceiver is selected from a set comprising a Wi-Fitransceiver, a Bluetooth transceiver, a Z-wave transceiver, and a ZigBeetransceiver.
 6. The system of claim 5 wherein the logic circuit isimplemented at least partially in software at a remote computing device.7. The system of claim 1 further comprising a switch operativelyconnected to the analog circuit.
 8. The system of claim 7 wherein theswitch is operatively connected to the analog circuit through a firstauxiliary contact and a second auxiliary contact to provide forredundancy.
 9. The system of claim 8 wherein the analog circuit providesfor determining if the switch just opened or just closed.
 10. Anelectrical safety monitoring system comprising: a housing; an analogcircuit disposed within the housing and having line inputs forhardwiring a first line (L1), a second line (L2), a third line (L3), anda ground (GND), wherein each of the line inputs is a three-phaseconnection, wherein the analog circuit is configured to monitor ifvoltage exists between any two of the line inputs and further configuredto visually indicate presence or absence of voltage on each of the lineinputs; a heartbeat circuit electrically connected to the analog circuitto provide a heartbeat signal indicative of voltage present on any ofthe line inputs, the heartbeat signal encoding state information for theline inputs; an isolated voltage source electrically connected to theheartbeat circuit to power the heartbeat circuit with a VDC+ and a VDC−;and a logic circuit in operative communication with the heartbeatcircuit for monitoring input from the heartbeat circuit and decoding theinput from the heartbeat circuit to determine state information for theline inputs; wherein the heartbeat signal is set to the VDC+ for x/2time and set to the VDC− for x/2 time, wherein x is defined as a totalcycle time of the heartbeat signal; wherein if there is an absence ofvoltage then the heart beat signal is set to the VDC+ for x/4 and set tothe VDC− for (3*x)/4.
 11. The system of claim 10 wherein the isolatedvoltage source is supplied by a programmable logic circuit (PLC). 12.The system of claim 10 further comprising a wireless transceiverelectrically connected to the heartbeat circuit for receiving theheartbeat signal and wherein the logic circuit is located remotely fromthe heartbeat circuit.
 13. The system of claim 12 wherein the wirelesstransceiver is selected from a set comprising a Wi-Fi transceiver, aBluetooth transceiver, a Z-wave transceiver, and a ZigBee transceiver.14. The system of claim 13 wherein the logic circuit is implemented atleast partially in software at a remote computing device.
 15. The systemof claim 10 further comprising a switch operatively connected to theanalog circuit.
 16. The system of claim 15 wherein the switch isoperatively connected to the analog circuit through a first auxiliarycontact and a second auxiliary contact to provide for redundancy. 17.The system of claim 16 wherein the analog circuit provides fordetermining if the switch just opened or just closed.